Flashing On and off LED's

Discussion in 'The Projects Forum' started by Lana89, Feb 11, 2014.

  1. Lana89

    Thread Starter New Member

    Feb 3, 2014
    3
    0
    Hello,

    I am trying to make 120 (4 rows and 30 columns) LED's go on and off alternatively. (At every given point in time 60 LED's are turned on and 60 off)

    Components and Parameters : Function Generator : AFG 300; Switch Dg202b http://www.vishay.com/docs/70037/dg201b.pdf; Op amp-741Cn; transistor (Using 8 transistors) : MJH6284 http://http://www.onsemi.com/pub_link/Collateral/MJH6284-D.PDF; LED: BXRA-C0402 (Need a minimum of 7V to light up) http://www.leds.de/out/media/67920.pdf

    I am using: A square pulse from a function generator (1Hz and 5V) A switch to control each row An op-amp to invert the square pulse (resulting in the alternating On and Off) The rows are connected in parallel (L1 to L3 to L5 to L7....L29 AND L2 to L4 To L6 To L8...L30). The columns are connected in series (L1 to L2 to L3 to L4) and are controlled by switches as shown in the image

    The switches are placed in so that either a row(s) or column(s) can be turned on and off

    I am supplying 5V at the base of the transistor through the switch (and op-amp depending on the light, L2 to L4 To L6 To L8...L30), +10 at the collector and -10 at the emitter.

    The Problem: when I connect a single transistor to my circuit, the square pulse is 5V, as i increase the number of transistors the voltage given by the function generator reduces, which in turn reduces the luminescence of my LED's (some don't even light up).

    I am using a 10 amp AC-DC powersupply

    I am not at liberty to change the components and the LED's are pre-wired, how do I get the maximum luminescence for all the LED's (at 9V and 15 Amp for the rows, and accordingly for the columns)

    Where am I going wrong?? (NEED HELP ASAP):(:confused::mad:

    thanks!
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    It would help if you could show all the component values.
     
  3. arouse1973

    New Member

    Feb 11, 2014
    4
    0
    You have two problems. One is not as bad as the other. Your current limiting resistor is in the wrong place. You will be driving the LEDs from the signal generator and not the transistor. This is why the LEDs dim. The other problem is you need an individual resistor for each LED otherwise if thermal runaway happens you could damage some of the LEDs.
    Adam
     
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